Clinical methods for analyzing the condition of blood include blood coagulation tests, for example. As general blood coagulation tests, blood coagulation tests represented by the prothrombin time (PT) and the activated partial thromboplastin time (APTT) are known. According to these methods, a blood sample is centrifuged, and a protein that is contained in the resulting blood plasma and involved in the coagulation reaction is analyzed. This field has already been technically established, and it has been believed that the needs in the medical front are almost satisfied.
However, in the perioperative (acute stage) treatment, for example, which requires promptness, in order to satisfy the needs of testing the patient's comprehensive disease states of coagulation accurately in a simple manner, the above methods are insufficient. Specifically, for example, in large-scale surgical operations such as heart surgery accompanied by extracorporeal circulation using an artificial heart-lung machine, serious traumatotherapy, and liver transplantation, in addition to surgical bleeding, bleeding resulting from abnormal coagulation may continue. In spite of this, in conventional coagulation tests, cell components such as platelets and erythrocytes, which play important roles in the in-vivo coagulation reaction, are removed by centrifugation. Therefore, it often happens that the test results are inconsistent with the actual clinical disease states.
In addition, the disease states of coagulation in the patient significantly vary through the perioperative period, and a bleeding tendency often turns into a thrombosis tendency. However, PT and APTT are tests for bleeding tendencies, and a high-sensitivity testing method for thrombosis tendencies has not yet been established.
As a comprehensive coagulation test in the acute stage, thromboelastometry, which dynamically measures changes in viscoelasticity accompanying the process of blood coagulation, has been commercialized by European and American companies under TEG® and ROTEM®. However, with respect to these products, there are issues such as (1) the measurement has not been automated, and the test results depend on the measurer's manipulation, (2) the measurement is susceptible to vibration, (3) the quality control (QC) procedure is complicated, and the reagent therefor is expensive, (4) the interpretation of output signals (thromboelastogram) requires skill, etc. These are considered to be the primary cause that hinders sufficient spread. Therefore, under the present circumstances, even for patients who would not need blood transfusion if subjected to a comprehensive coagulation test, blood preparations are often used for preventive and experimental purposes. This not only increases the risks of infectious diseases but also wastes blood preparations and increases the medical cost.
In recent years, a technology for evaluating the degree of blood coagulation accurately in a simple manner has been developed. For example, Patent Document 1 discloses a technology for obtaining the information about blood coagulation from the permittivity of blood, and describes “a blood coagulation system analysis device, including: a pair of electrodes; an application means for applying an alternating voltage to the pair of electrodes at predetermined time intervals; a measurement means for measuring the permittivity of blood placed between the pair of electrodes; and an analysis means for, using the blood permittivity measured at the time intervals after the cancellation of the effect of an anticoagulant on the blood, analyzing the degree of action of the blood coagulation system.”
As a blood specimen in this method, generally, blood collected from the vein using an anticoagulant such as citric acid is used. Immediately before the start of measurement, the anticoagulation effect is canceled using an anticoagulation treatment canceling agent such as an aqueous calcium chloride solution, and the measurement is performed with the blood coagulation reaction being promoted.